Method and Apparatus for Recording One-Step, Full-Color, Full-Parallax, Holographic Stereograms

ABSTRACT

Holographic stereograms and holographic optical elements are printed using computer rendered images of 3D computer models or processed images. Printing of one-step, full-color, full-parallax holographic stereograms uses a reference beam-steering system to expose a holographic recording material from different angles by a reference beam. A coherent beam is split into object and reference beams that interfere with each other at an elemental hologram on a holographic recording material. A voxel-control lens can be placed in the path of the object beam and in close proximity to the holographic recording material to control resolution of a holographic stereogram. Interchangable band-limited diffusers and reference-beam masking plates, and viewing zone techniques can be used in the rendering process.

This application claims the benefit of U.S. Provisional Application No.60/076,237, filed Feb. 27, 1998.

1. BACKGROUND OF THE INVENTION

The present invention relates generally to the field of holography. Moreparticularly, it concerns methods and devices for creating and printingvariable size and variable resolution holographic stereograms andholographic optical elements using computer rendered images ofthree-dimensional computer models or using computer processed images.

A holographic stereogram is a type of hologram synthesized or composedfrom a set of two-dimensional views of a subject. A holographicstereogram is capable of creating the convincing illusion of a solidthree-dimensional subject from closely spaced, discrete-perspective,two-dimensional component views. In addition, if the two-dimensionalcomponent views are properly generated, a holographic stereogram canalso create the illusion of an animated image. Although holographicstereograms can project such special effects, due to limitations in themethods and techniques for printing holographic stereograms, holographicstereograms have generally been expensive, difficult, and time consumingto produce.

Techniques have been developed for reducing the number of steps involvedin producing holographic stereograms to one optical printing step.One-step technology usually involves using computer processed images ofobjects or computer models of objects to build a hologram from a numberof contiguous, small, elemental pieces, known as elemental holograms orhogels. This one-step technology eliminates the need to create apreliminary hologram.

To produce a full-parallax, holographic stereogram using traditionalone-step technology, a three-dimensional computer model of an object ora scene is created. There are numerous computer graphic modelingprograms, rendering programs, animation programs, three dimensionaldigitalization systems, or combinations of the programs or systems thatcan be used to generate and manipulate a three-dimensional computermodel of an object or a scene. Examples of such programs or systemsinclude, but are not limited to computer-aided-design (CAD) programs,scientific visualization programs, and virtual reality programs.

In addition, to produce a holographic stereogram using one-steptechnology requires that the position of the hologram surface andindividual elemental holograms relative to an object or a scene bedetermined. Furthermore, a proper computer graphic camera(s)'sdescription for an elemental hologram and the size and location of aspatial light modulator (SLM), a device that can display atwo-dimensional image, need to be determined.

Once all the aforementioned initial parameters are determined, atwo-dimensional projection on the SLM for each elemental hologram iscomputed based on the computer graphic model of the object or scene thatwas created, the positions of the elemental holograms, and the computergraphic camera's description for the elemental holograms. Thetwo-dimensional projection on the SLM for each elemental hologram may berendered using various computer graphic techniques. The process ofcreating two-dimensional views from a three-dimensional object andadding qualities such as variations in color and shade to a computergraphic model is often referred to as rendering. There are numerousmethods for rendering. One method is ray-tracing, which computes imagesby accurately simulating sampled light rays in a computer model. Anothermethod is scan-line conversion, which computes images one raster or lineat a time. Typically scan-line rendering does not produce as realisticresults as ray tracing. However, scan-line rendering is frequently usedin animation packages because it is faster. Another method for usingcomputer graphics to render images for one-step, full-parallaxholographic stereograms is described in an article by Halle and Kropp.Halle, M. and Kropp, A., “Fast Computer Graphics Rendering for FullParallax Spatial Displays,” Proc. Soc. Photo-Opt. Instrum. Eng. (SPIE),3011:105-112 (Feb. 10-11, 1997), the disclosure of which is incorporatedherein by reference.

When holographic stereograms are produced by either the multi-step orone-step techniques, the reconstructed images may have geometric imagedistortions. These geometric image distortions may be very apparent,especially in large, billboard size holographic displays or holographicdisplays in other geometries, such as an alcove or a partial cylinder.

One solution that has been incorporated into multi-step techniques tocorrect for geometric image distortions for multiplex holograms isdiscussed in an article by Okada. Okada, K., et. al., “A Method ofDistortion Compensation of Multiplex Holograms,” Optics Communications,vol. 48, no. 3, pp. 167-170 (Dec. 1, 1983), the disclosure of which isincorporated herein by reference. The technique discussed in Okada'sarticle to correct distortion is a method to correct geometrical andtime distortion of a single or monocular viewpoint of a finishedhologram. Because it is a post-processing method that takes place afterimage acquisition, Okada's technique would be inefficient if adopted togenerate animated computer graphics for one-step, holographicstereograms. Moreover, Okada's method only produceshorizontal-parallax-only transmission type holograms.

Others have developed techniques for pre-distorting one-step,holographic stereograms to reduce distortion in the final holographicdisplay. One such pre-distortion technique is described in a paper byHalle and others. Halle, M. et al, “The Ultragram: A GeneralizedHolographic Stereogram,” Proc. Soc. Photo-Opt. Instrum. Eng. (SPIE),vol. 1461, Practical Holography V, p. 142 (February 1991), thedisclosure of which is incorporated herein by reference. Although widelyused, typical pre-distortion techniques for one-step methods forproducing full-parallax, holographic stereograms are significantlylimited by available computer processing speeds and the resolution ofimages produced by traditional one-step methods. In addition, techniquesfor pre-distorting one-step, full-parallax, holographic stereograms havenot been able to produce comprehensible, animated, one-step,full-parallax, holographic stereograms.

Apparatus for printing one-step, monochromatic, holographic-stereogramshave been developed. Typically, such prior art printers, as depicted inFIG. 1, include: a monochrome coherent light source 1, lenses 42,mirrors 40, an optical system 89, a shutter 10, a mechanism fortranslating film 69, holographic recording material 70, usually in theform of film, a personal computer 85 to control the timing for theexposure sequence, and a separate high-speed computer 87 for imagecalculations. The prior art printer depicted in FIG. 1, was discussed intwo articles by Yamaguchi. Yamaguchi, M. et al., “Development of aPrototype Full-Parallax Holoprinter.” Proc. Soc. Photo-Opt. Instrum.Eng. (SPIE), vol. 2406, Practical Holography IX, pp. 50-56 (February1995); and Yamaguchi, M., et al., “High-Quality Recording of aFull-Parallax Holographic Stereogram with a Digital Diffuser,” OpticsLetters, vol. 19, no. 2, pp. 135-137 (Jan. 20, 1994), the disclosures ofeach are incorporated herein by reference. The prior art printerdepicted in FIG. 1 is capable of producing monochromatic holographicstereograms, but not full-color holographic stereograms.

A typical prior art hologram printer, like the one depicted in FIG. 1,usually is supported by a vibration isolation table 80. In addition, theprior art printer depicted by FIG. 1 uses a HeNe laser for a lightsource 1 that produces a coherent light beam 5 that may be collimated. Ashutter 10 is placed at the output of light source 1. A beam-splitter 15splits the light 5 from the light source 1 into an object beam 20 and areference beam 25. The polarization of the object and reference beams20, 25 are adjusted by a pair of half-wave plates 30 and a pair ofpolarizers 35. The half-wave plates 30 and polarizers 35 also controlthe ratio of the beams. The prior art printer also uses a number ofmirrors 40. In addition, the prior art printer uses a system ofenlarging lenses 42 to distribute the object beam 20 from the lightsource 1 into the optical system 89 depicted in FIG. 1.

The optical system 89 of the prior art printer of FIG. 1 includes aband-limited diffuser 45, a liquid crystal display panel (LCD panel) 50,and a converging lens 55. A band-limited diffuser is a diffuser with adeterministic phase pattern designed to diffuse light in a specificpattern or direction. The band-limited diffuser 45 depicted in FIG. 1 isspecifically designed for the monochromatic light source being used—aHeNe laser. The LCD panel 50 used in the prior art printer of FIG. 1 isa gray scale, electrically addressed panel with twisted-nematic liquidcrystals. The LCD panel 50 receives image data calculated by ahigh-speed computer 87 by an analog video signal. The converging lens 55shown in FIG. 1 focuses the images from the LCD panel 50 to theholographic recording material 70. The converging lens 55 generally hasa low f-number in order to produce a wide angle of view. Due to the needto correct for spherical aberrations along the optical axis, Yamaguchiutilized a converging lens 55 composed of three lenses to reducespherical aberration and realize a f-number of around 0.8.

To prevent the exposure of parts of the holographic recording material70 that are not part of the elemental hologram 110 meant to be exposed,the prior art printer of FIG. 1, uses, in close proximity to theholographic recording material 70, an object beam masking plate 60 withan aperture the size of the elemental hologram 110 to prevent the objectbeam 20 from exposing other parts of the holographic recording material70.

The band-limited diffuser 45 shown in FIG. 1 improves the uniformity ofthe distribution of the object beam 20 over an elemental hologram on theholographic recording material 70. If the band-limited diffuser 45 isdesigned such that an object beam 20 is focused only over the area of anelemental hologram, then an object beam masking plate 60 is not neededto prevent exposure of areas outside the elemental hologram. However, ifused with such a band-limited diffuser, the object beam masking plate 60may have an aperture larger than the size of the elemental hologram 110.An object beam 20 and a band-limited diffuser 45 that allow evenillumination of an elemental hologram 110 by an object beam 20 need tobe matched by a reference beam masking plate 65 with an aperture thesize of the elemental hologram 110. Because the required matching of aobject beam 20, a band-limited diffuser 45, and reference beam maskingplate 65 to the size of a desired elemental hologram, it has beendifficult to change the sizes of elemental holograms exposed by ahologram printer. Because of this lack of flexibility, prior artprinters cannot easily print holograms having different sizes ofelemental holograms, and are restricted to printing holograms withsingle, fixed-sized elemental holograms.

FIGS. 2-4 illustrate alternative prior art embodiments of opticalsystems that function in the same way as the optical system 89 depictedin FIG. 1.

In FIGS. 2-4, an object beam 20 is directed through a SLM 90 that has asample image point 100 on its surface. The object beam 20 may be normalto the SLM surface or off-axis from the normal. SLM 90 may also have anarray of pixels 95. LCD panels, cinematography film, and transparencieshave been used as SLMs 90.

In FIG. 2, the object beam is directed through a simple diffuser 105,such as a section of ground glass, that scatters light. When a simplediffuser 105 is used, then an object beam masking plate 60 must be usedto prevent exposing areas of the holographic recording material 70outside of the elemental hologram 110 that are not meant to be exposed.

In FIG. 3, an object beam 20 is directed through a holographic opticalelement (HOE) 115. A HOE is a hologram that is specially designed toredirect light emanating from a source in a certain way. For instance, aHOE may be designed to act as a lens to converge light to a singlepoint. As another example, a HOE may be designed to act as aband-limited diffuser that is paired with a lens to converge light overan area rather than at a single point. The HOE 115 depicted in FIG. 3 isone that is designed to evenly expose an area the size and shape of anelemental hologram 110. When such a HOE is used, an object beam maskingplate 60 (shown in FIG. 2) need not be used at all or, if used, may havean aperture larger than the size of the elemental hologram 110 to beexposed.

In FIG. 4, an object beam 20 is directed through a band-limiteddiffuser, which may be a band-limited digital diffuser, 45 and aconverging lens 55. The band-limited diffuser 45 depicted in FIG. 4 isdesigned to converge the object beam 20, over the area of elementalhologram 110. Thus, an object beam masking plate 60 (shown in FIG. 2)need not be used at all or, if used may have an aperture larger than thesize of the elemental hologram 110 to be exposed.

In FIGS. 2-4, the sample image point 100 is an image point of the SLM 90that is recorded in an elemental hologram 110 on a holographic recordingmaterial 70. Reference beam 25 is directed at the elemental hologram 110such that the interference pattern formed by the interaction of theobject beam 20 and the reference beam 25 may be recorded on theelemental hologram 110 on the holographic recording material 70.

To expose a two-dimensional array of elemental holograms, the prior artprinter of FIG. 1 uses a mechanism for translating holographic film 69that includes pulse controlled motors 71. Typically, the holographicrecording material 70 in a prior art printer is photographic film. Thefilm is held between the object beam masking plate 60 and the referencebeam masking plate 65. Both masking plates 60 and 65 have apertures thatare the size of the elemental holograms 110 being exposed. The maskingplates 60 and 65 are moved by a solenoid 72. Pulse controlled motors 71translate the film in two directions.

In the prior art system depicted in FIG. 1, the timing of the exposuresequence is controlled by a personal computer. Thus, the solenoid 72, aswell as the pulse controlled motors 71 and the shutter 10, arecontrolled by the personal computer 85. In contrast, the images for theexposures are calculated off-line by a high-speed computer 87. The imagecalculations are transferred by an analog video signal to the LCD panel50.

For a holographic stereogram to be reconstructed, an illumination sourcemust be placed at an appropriate angle. If the illumination source isnot placed correctly, a holographic stereogram will not be reconstructedor will appear with distortions, such as magnification distortions.Despite advances in holographic techniques and equipment, the displayillumination geometry of a one-step, holographic stereogram remains aproblem. The display illumination geometry, i.e., the placement of anillumination source with respect to a holographic stereogram, depends onthe cumulative effect of the angles at which a reference beam exposedeach of a holographic stereogram's elemental holograms. For example, ifthe angle at which all of the elemental holograms on a holographicstereogram are exposed to a collimated reference beam is constant, andif the surface of the holographic stereogram is flat, then theholographic stereogram needs a collimated illumination source toilluminate each of the elemental holograms from the appropriate angle ifthe hologram is to be properly reconstructed without defects such asmagnification distortion.

Furthermore, in practice, it has been common to create reflectionholographic stereograms which are meant to be illuminated with adiverging light source such as a point source. However, the prior arthas not overcome the difficulty in designing a printer in which theangle of a reference beam is automatically and flexibly changeable toallow reconstruction by a point source and with minimal distortion.

In addition, it remains difficult to control the resolution or elementalhologram density of a holographic image. The sharpness of a holographicimage depends on the image resolution and the extent of any blurring.Blurring can be caused by having a large illumination source, such asthat of a long florescent light, illuminate a hologram. In addition,blurring can be caused by the large spectral spread of an illuminationsource. If an illumination source that is small and monochromatic, suchas a laser source expanded through a microscope objective lens (i.e. asmall, inexpensive, achromatic, high-power lens), is used, blurring maybe minimized, and the sharpness of the holographic image will mainlydepend on the image resolution of the hologram.

The image resolution of a three-dimensional image is defined as thevolumetric density of individually distinguishable image points in animage volume. For one-step, holographic stereograms, includingfull-parallax and horizontal-parallax holograms, this resolution isusually not constant throughout an image volume. For small images oflittle depth, the variation of image resolution with depth is hardlynoticeable. However, for holographic stereograms with significant depth,the variation in image resolution with depth can be very apparent.

As shown in FIG. 5, if the light from an illumination source 130 that isthe same type of light source as that which generated the reference beam25 that exposed an elemental hologram 110 illuminates the elementalhologram 110 from the appropriate conjugate angle, the reconstruction125 of the sample image point 100, (shown in FIGS. 2-4), on thereconstruction 120 of the image of the SLM is formed at the sameapparent distance and position relative to the elemental hologram 110 asit appeared to the elemental hologram 110 at the time of recording.

FIG. 6 shows lines drawn from the boundaries between neighboringelemental holograms 110 on a holographic recording material 70 throughthe boundaries between neighboring reconstructed pixels 135 of thereconstructed image 120 of a SLM. The areas bounded between the linesdrawn from the boundaries of at least two elemental holograms representindependently addressable volume elements, or voxels 140. A voxel 140 isa component unit which represents an arbitrary three-dimensional objector scene. Assuming that the elemental holograms 110 are larger than theSLM pixels, as shown in FIG. 6, the sizes of the voxels 140 increasewith increasing distance from the surface of a reconstructed image of aSLM 120. If the sizes of the voxels 140 are too coarse relative to thedesired detail size of a three-dimensional object or scene, thereproduced image will be poor or indiscernible. If the three-dimensionalimage of an object or scene extends over a wide range of depth, avariation in the sizes of the voxels will also be very undesirablebecause such a variation would lead to poor image quality.

Thus, hologram printers of the prior art have limitations that make themimpractical for commercial purposes. In particular, these prior artprinters suffer from: lack of ability to print full-color holographicstereograms; lack of ability to simultaneously expose multiple elementalholograms; lack of flexibility to quickly and easily adjust a hologramprinter to print at different elemental hologram sizes; lack offlexibility to easily change the angle of a reference beam to aholographic recording material; lack of ability to control theresolution of a hologram; and lack of ability to create computergenerated images which display animation or different images with achange of viewing position.

SUMMARY OF THE INVENTION

The present invention overcomes many of the above-noted limitations andproblems of prior art hologram printers and methods used to printholographic stereograms with the following structures and methods.

The present invention is an apparatus and method for printing one-step,full-color, full-parallax holographic stereograms utilizing a referencebeam-steering system that allows a reference beam to expose aholographic recording material from different angles. More particularly,a coherent beam is split into object and reference beams. The objectbeam passes through an object beam unit in which a rendered image isdisplayed, while the reference beam passes through the referencebeam-steering system. The object and reference beams interfere with eachother at an elemental hologram on a holographic recording material. Acomputer controls the exposure time and the movement of the recordingmaterial and may also render the images displayed in the object beamunit. In addition, the computer may also store the images before theyare displayed in the object beam unit.

In addition, the present invention may also utilize a voxel-control lensplaced in the path of the object beam and in close proximity to theholographic recording material to control the resolution of aholographic stereogram.

In addition, the present invention may also utilize interchangableband-limited diffusers and reference-beam masking plates.

Furthermore, the present invention incorporates viewing zone techniquesto the rendering process for one-step, holographic stereograms toproduce animated, one-step, holographic stereograms.

In accordance with long-standing patent law convention, the words “a”and “an” when used in this application, including the claims, denotes“at least one.”

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings form part of the specification and are includedto further demonstrate certain aspects of the present invention. Theinvention may be better understood by reference to one or more of thesedrawings in combination with the detailed description of specificembodiments presented herein.

FIGS. 1( a) and (b) are schematic, top-view drawings of a prior arthologram printer.

FIGS. 2( a) and (b) are simplified, top-view illustrations of aone-step, reflection, elemental hologram recording using an opticalsystem including a simple diffuser.

FIG. 3 is a simplified, top-view illustration of a one-step, reflection,elemental hologram recording using an optical system including aholographic optical element.

FIG. 4 is a simplified, top-view illustration of a one-step, reflection,elemental hologram recording using an optical system including aband-limited diffuser and a converging lens.

FIG. 5 is a simplified, top-view illustration of the reconstruction ofan elemental hologram of a holographic stereogram.

FIG. 6 is an illustration of the changes in sizes of voxels withdistance from a reconstructed image of a SLM.

FIG. 7 is a top-view, schematic drawing of one embodiment of the presentinvention for a one-step, full-color, full-parallax printer forholographic stereograms.

FIG. 8 is a top-view, schematic drawing of another embodiment of thepresent invention for a one-step, full-color, full-parallax printer forholographic stereograms.

FIG. 9 is an illustration of a particular embodiment of the presentinvention to control the variation in sizes of voxels.

FIGS. 10( a) and (b) illustrate how the apparent distance of a SLM, asseen by an elemental hologram, may change when a voxel-control lens isutilized.

FIG. 11 is an illustration of voxel boundary lines that areapproximately parallel to each other.

FIG. 12 is a schematic illustration of an embodiment of the referencebeam-steering system of the present invention.

FIG. 13 is a schematic illustration of another embodiment of thereference beam-steering system of the present invention.

FIG. 14 is a schematic illustration of an embodiment of the referencebeam-steering system of the present invention that utilizes abeam-steering aperture.

FIG. 15 is an orthogonal-view illustration of an embodiment of thebeam-steering mirror system of the present invention.

FIG. 16 is a front-view illustration of another embodiment of thebeam-steering mirror system of the present invention.

FIG. 17 is a schematic illustration of an embodiment of the referencebeam-steering system of the present invention that utilizes fiber opticsand a translation system.

FIG. 18 is a simplified, orthogonal-view illustration of an embodimentof the reference beam-steering system of the present invention thatutilizes fiber optics and a translation system.

FIG. 19 is a simplified, orthogonal-view illustration of an embodimentof a reference beam-steering system of the present invention thatutilizes fiber optics, a translation system, and a optical combinerunit.

FIG. 20 is a schematic illustration of an object beam unit of thepresent invention that utilizes fiber optics.

FIG. 21 is a top-view, schematic drawing of one embodiment, whichutilizes fiber optics, of the present invention for a one-step,full-color, full-parallax printer for holographic stereograms.

FIG. 22 is a simplified, orthogonal-view illustration of an embodimentof a material holder of the present invention.

FIG. 23 is a schematic illustration of an embodiment of the presentinvention with fixed object beam units and fixed reference beam-steeringsystems.

FIG. 24 is a schematic illustration of an embodiment of the presentinvention with mobile object beam units and mobile referencebeam-steering systems.

FIG. 25 is a schematic illustration of another embodiment of the presentinvention with mobile object beam units and mobile referencebeam-steering systems.

FIG. 26 is a schematic illustration of yet another embodiment of thepresent invention with mobile object beam units and mobile referencebeam-steering systems.

FIGS. 27( a), (b), and (c) are orthogonal-view illustrations ofremovable band-limited diffusers and removable reference beam maskingplates.

FIG. 28 is a flow chart illustrating the steps for creating an animated,one-step, full-parallax holographic stereogram.

FIG. 29 is an illustration of viewing zones for a holographic stereogramthat displays different images when viewed from different viewing zones.

FIG. 30 is an illustration of rays projecting from the perimeter ofviewing zones.

FIG. 31 is an illustration of viewing zone mask volumes.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The following examples are included to demonstrate illustrativeembodiments of the present invention. It should be appreciated by thosewith skill in the art that the techniques disclosed in the followingexamples represent techniques discovered by the inventors to functionwell in practice and thus can be considered to constitute exemplarymodes for its practice. However, those with skill in the art will, inlight of the present disclosure, appreciate that many changes can bemade in the specific embodiments which are disclosed and still obtain alike or similar result without departing from the spirit and scope ofthe invention. For instance, a HOE or other appropriate optics mayreplace the combination of a lens and a band-limited diffuser. Inaddition, a HOE may also replace a lens or a combination of lenses.Furthermore, SLMs may include, but are not limited to LCD panels,digital micro-mirror arrays, film, or transparencies. In addition,computer storage devices may include, but are not limited to hard disks,static or dynamic RAM, flash memory, DVD drives, or tape drives.Moreover, motors may include, but are not limited to DC servo motors,stepper motors, or actuators.

The present invention provides a system and method for printingone-step, full-color, full-parallax holographic stereograms. Somepresently illustrated embodiments are depicted in FIGS. 7-31.

One embodiment of the present invention for a printer is illustrated inFIG. 7. As depicted in FIG. 7, most of the parts of the printer, exceptfor a computer 230 and controllers 305 and 455, are isolated fromvibrations by, for example, being supported on vibration isolation table80. The table 80 may be composed of steel with a honeycomb interior. Thelegs of the table 80 may be air pistons which can absorb vibrations.Other types of vibration isolation may also be acceptable. In someembodiments, the computer 230 and controllers 305 and 455 may besupported on table 80. The computer 230 may have multiple ports andserial or parallel cables through which the computer 230 can controldevices, like motor controllers, or through which the computer 230 cansend output, such as images. In addition, computer 230 may havecomputational power and speed sufficient for three-dimensional computergraphics. Furthermore, computer 230 may include one or more centralprocessing unit and may include one or more storage devices, forexample, hard disks, a redundant array of independent disks, FLASHmemory, or static or dynamic RAM, in which rendered images are stored.If more than one central processing unit is used, they may operateindependently or in parallel. If more than one storage device is used,they may also operate independently or in parallel. In some embodiments,lasers 200 are not supported by table 80. The lasers 200 may be lasersof three different colors. For example, one laser 200 may be a kryptonion or a HeNe laser to produce a red beam of light, another laser 200may be an argon ion or a YAG laser to produce a green beam of light, anda third laser 200 may be an argon ion or a HeCd laser to produce a bluebeam of light. Other light wavelengths are also acceptable. In addition,lasers 200 may be solid state diodes or other types of lasers. The beamsof light from the lasers 200 may go through open air. In addition, thebeams of light from the lasers 200 may go through pipes so thatinstabilities due to air currents will be reduced. Also, the beams maybe transmitted through polarization-preserving optical fibers.

In FIG. 7, the coherent light beams 5 produced by the lasers 200 aredirected at variable beam splitters 205. Variable beam splitters arehalf-mirrors that split a beam by reflecting part of the beam andtransmitting most of the rest of the beam. If fiber optics are used totransmit beams, then fiber optic beam splitters that work by contactingtwo parallel fibers together and letting the light from the fiberscouple may be used. The coherent light beam 5 from each of the lasers200 is split into two beams, an object beam 20 and a reference beam 25.In some embodiments, each object beam 20 and each reference beam 25 maybe directed through half-wave plates 30 and polarizers 35. In otherembodiments, if polarization-retaining fiber optic cables are used totransmit a beam and if the cables are rotatable about their center axes,half-wave plates 30 need not be used. If needed, each object beam may bereflected off one or more mirror 40. The mirrors 40 of the presentinvention may be, for example, first surface or front surface mirrors.Each object beam 20 may be directed through a low pass spatial filter220 to remove unwanted noise. A low pass spatial filter 220 may includea microscope objective lens and a pinhole. Each object beam 20 may thenpass through a beam shutter 225. In one embodiment, the beam shutters225 may be high-speed, mechanical iris shutters, for example, those usedin made the photography industry. In other embodiments, the beamshutters 225 may be electro-optical systems such as liquid crystal cellsor acousto-optical modulator crystals. In another embodiment, instead ofusing separate beam shutters 225, the SLM 90 in the object beam unit,generally 700, can function as a shutter for all three object beams. Theshutters 225 are controlled by the computer 230. The object beams 20 maybe then directed through an object beam unit 700. In the object beamunit 700, the object beams 20 may be directed such that the object beams20 converge at the plane of a SLM 90. SLM 90 may include, but is notlimited to, a transmissive LCD panel, a reflective LCD panel, anoptically addressed LCD panel, a digital micro-mirror array, film, aprojection or a transparency. The SLM 90 may receive image input by avideo cable from the computer 230. In addition, multiple SLMs mayreceive images generated in parallel by multiple central processingunits. Moreover, multiple SLMs may receive images from the storagedevice or devices of computer 230. After passing through the SLM 90, theobject beam 20 may pass through a HOE 115, or another system, like thoseillustrated in FIGS. 2-4, that is designed to converge the object beamand evenly expose an area the size of an elemental hologram. In oneimplementation, the HOE 115 may be a transmission-type hologram that canconverge three different monochromatic object beams at slightlydifferent angles onto the elemental holograms to be exposed withoutallowing zeroth-ordered light from any of the object beams to intersectthe elemental holograms to be exposed. After passing through the objectbeam unit 700, the object beam 20 may then be transmitted through avoxel control lens 500 and may then expose an elemental hologram 110 ona holographic recording material 70 in a material holder 300. Theholographic recording material 70 may be, but is not limited to, apan-chromatic photopolymer, a pan-chromatic or monochromatic silverhalide photographic emulsion, dichromated gelatin, or other suitablephotopolymers. The holographic recording material 70 may be heldsecurely by a material holder 300 that may be able to translate theholographic recording material in two directions. The movement of thematerial holder 300 may be controlled by film holder motor controller305 which may be controlled by computer 230.

As further depicted in FIG. 7, after the beams are split into objectbeams 20 and reference beams 25 by the variable beam splitters 205, eachof the reference beams 25 passes through a variable attenuator 210 whichallows the intensity of each reference beam 25 to be independentlyadjusted. The reference beams may be reflected off of a mirror 40 beforepassing through dichroic combiners 215 or other suitable opticalcombiners. A dichroic combiner is a wavelength selective mirror whichreflects some wavelengths, but is transparent to other wavelengths. Thedichroic combiners 215 in FIG. 7 combine the three reference beams 25into one beam which may then pass through a beam shutter 225 beforepassing through a low pass spatial filter 220. The reference beam 25then passes through a reference beam steering system 400 which controlsthe angle which the reference beam 25 intersects with the holographicrecording material 70. A beam-steering mirror system of the referencebeam-steering system is controlled by a mirror system motor controller455 that is controlled by computer 230.

Furthermore, the present invention allows separate elemental hologramsto be printed in different colors. For instance, by placing a beamshutter in the path of each object beam and reference beam and thenselectively closing the beam shutters, one elemental hologram may beexposed to only red object and reference beams, another may be exposedto only green object and reference beams, and another may be exposed toonly blue object and reference beams.

An embodiment of the present invention in which multiple elementalholograms are simultaneously exposed is depicted in FIG. 8. The beamsfrom lasers 200 are split by variable beam splitters 205 and then afterbeing reflected by mirrors 40 are split again by additional variablebeam splitters 205, thereby forming two or more object beams 20 and twoor more reference beams 25 from each laser 200. In other embodiments,the beams from lasers 200 may be split even more times to form moreobject beams 20 and more reference beams 25. Each object beam 20 passesthrough a low pass filter 220 and a beam shutter 225. Each set of threeobject beams 20 may be reflected by mirrors 40 and pass through a SLM90, a HOE 115, and a voxel control lens 500 to expose an elementalhologram 110 on a holographic recording material 70 held by a materialholder 300. The movement of the material holder 300 is controlled byfilm holder motor controllers that are controlled by computer 230. Eachset of three reference beams 25 passes through variable attenuators 210and are combined into a beam by a dichroic combiner 215 or othersuitable optical combiners. Each of the resulting two reference beams 25passes through a beam shutter 225 and a low pass spatial filter 220.Each reference beam 25 then passes through a beam-steering system 400before hitting an elemental hologram 110. Thus, as depicted in FIG. 8,multiple elemental holograms may be simultaneously printed.

An embodiment of the present invention in which the variation in voxelsize is controlled is illustrated by FIGS. 9 and 10. As shown in FIGS. 9and 10, this control is accomplished by placing a voxel-control lens 500in the path of an object beam 20 between SLM 90 and holographicrecording material 70. The voxel-control lens 500 may be placed in closeproximity to holographic recording material 70. The voxel-control lens500 may be capable of making an SLM or a projected image of a SLM seenfrom the viewpoint of an elemental hologram 110 appear at a greaterapparent distance relative to the holographic recording material 70during recording, so that a sample image point 100 on the SLM 90 surfaceis reconstructed at a greater distance away from the holographicrecording material 70. FIG. 10( a) illustrates how an image 505 of a SLMmay appear to an elemental hologram 110 in a printer without avoxel-control lens. FIG. 10( b) illustrates how an image 505 of a SLMmay appear to an elemental hologram in a printer with a voxel-controllens 500. As shown in FIG. 10, the voxel control lens magnifies theimage 505 of a SLM, such that the angle α subtended by the image doesnot change but the angle φ subtended by an elemental hologram decreasesto θ when a voxel control lens is used. The distance between the image505 of a SLM and the holographic recording material 70 may be varied byvarying the focal length of the voxel-control lens 500 or its positionbetween the holographic recording surface 70 and the converging lens 55or other optical systems, including simple diffusers or HOEs, as shownin FIGS. 1-3, used in the prior art to converge light onto theholographic recording material 70. In some embodiments, the voxelcontrol lens 500 may be part of the object beam unit 700.

In one particular embodiment of this invention, it is possible to makethe voxel sizes fairly constant over a wide range of distances from aholographic recording material 70. This is accomplished by choosing avoxel-control lens 500 with a focal length equal to the distance betweenthe voxel-control lens 500 and the actual location of the SLM or thelocation of a projected image of the SLM as seen by an elementalhologram in a printer without a voxel-control lens. Such a voxel-controllens 500 and geometrical layout will effectively reconstruct the SLM 120at an infinite distance relative to holographic recording material 70.If the size of the pixels 95 on a SLM 90 are small compared to the sizeof the elemental holograms 110, the voxel 140 boundary lines for such anembodiment will no longer intersect close to the holographic recordingmaterial 70 as depicted in FIG. 6, but instead become approximatelyparallel lines which extend out to a great distance without intersectingas shown in FIG. 11.

Although the characteristics of a voxel-control lens 500 may depend onthe desired results, typically it is desirable for the voxel-controllens 500 to be achromatic and have an f-number of around 3.0 or lower.In one particular embodiment, the voxel-control lens may be achromaticand have an f-number of 2.4. In other embodiments, the voxel-controllens may have lower f-numbers, such as 0.5. Lower f-numbers aredesirable because they allow for a wider angle of view. In yet otherembodiments, the voxel-control lens may be monochromatic.

FIG. 12 depicts yet another embodiment of the present invention.Referring to FIGS. 12-16, a reference beam-steering system, generally400, may use a beam-steering mirror system 450 to direct a referencebeam 25, through a first beam-steering lens 410 and a secondbeam-steering lens 405 to an elemental hologram 110 on a holographicrecording material 70 which, if desired, may be inclined with respect tothe normal to the center axis 420.

The beam-steering mirror system, generally 450, may be embodied invarious ways. One particular embodiment is depicted in FIG. 15. In FIG.15, a deflection mirror 460 is fixedly mounted to a first rotatablemount 465, such that when the first rotatable mount 465 rotates, thedeflection mirror 460 rotates about a first axis 451 which passesthrough center point 461 of the deflection mirror 460. A motor for thefirst rotatable mount 470, which is controlled by a motor controller455, rotates the first rotatable mount 465. The motor for the firstrotatable mount 470 is fixedly attached to a support 475. Firstrotatable mount 465 is rotatably mounted to a support 475 with bearingsor bushings to allow the first rotatable mount 465 to rotate about thefirst axis 451. Support 475 is fixedly mounted by an attaching device ona second rotatable mount 480 such that when the second rotatable mount480 rotates, the deflection mirror 460 rotates about a second axis 452which passes through the center point 461 of the deflection mirror 460and which is orthogonal to the first axis 451. A motor for the secondrotatable mount 485, which is controlled by a motor controller 455,rotates the second rotatable mount 480. The motor for the secondrotatable mount may be fixedly attached to a vibration isolation table80. The motors for the first and second rotatable mounts, 470 and 485,may be, but are not limited to, stepper motors or DC servo motors. Thesame or a separate motor controller 455 controlled by computer 230 maycontrol the motors for the first and second rotatable mounts 470 and480.

Another embodiment of a beam-steering mirror system 450 is a deflectionmirror attached to a gimbal mount. In FIG. 16, a deflection mirror 460is fixedly mounted to a first axle 490 such that the deflection mirror460 rotates about a first axis 451 which passes through the center point461 of the deflection mirror 460. First axle 490 is rotated by a motor491 for the first axle which is controlled by a motor controller 455.The motor 491 for the first axle is fixedly attached to a first gimbalmount 494. First axle 490 is rotatably mounted by bearing or bushing tothe first gimbal mount 494. The first gimbal mount 494 is fixedlymounted by an attaching device to a second axle 492 at the opposite endsof a diameter of the first gimbal mount 494 that coincides with a secondaxis 452. Second axle 492 is rotated by a motor 493 for the second axleand is controlled by a motor controller 455. The deflection mirror 460rotates about the second axis 452 which passes through the center point461 of the deflection mirror 460 and which is orthogonal to the firstaxis 451. Second axle 492 is rotatably mounted by bearing or bushing toa second gimbal mount 496. The motors 491 and 493, for the first andsecond axles, 491 and 493, may be, but are not limited to, steppermotors or DC servo motors. The same or separate motor controllers 455,controlled by a computer 230, may control the motors for the first andsecond axles, 491 and 493.

As shown in FIGS. 12-16, the center axis 420 of the beam-steering lenses405, 410 intersects the first axis 451 and the second axis 452 andpasses through the center of an elemental hologram. A reference beam 25may be directed at the center point 461 of the deflection mirror 460. Acomputer 230 controls the mirror system motor controller or controllers455 of the beam-steering mirror system 450, such that a reference beam25 reflected off the deflection mirror 460 hits an elemental hologram110 on a holographic recording material 70 at a desired angle. Thedeflection mirror 460 may be placed at a distance of one focal length411 of the first beam-steering lens away from a first beam-steering lens410. The first beam-steering lens 410 may be placed at a distance of thesum of the focal length 411 of the first beam-steering lens and thefocal length 406 of the second beam-steering lens away from the secondbeam-steering lens 405. The second beam-steering lens 405 may be placedat a distance of one focal length 406 of the second beam-steering lens,away from the holographic recording material 70. The beam-steeringsystem 400 of the present invention allows the reference beam 25 to besteered to intersect with elemental holograms 110 at different angles.

In another embodiment, depicted in FIG. 13, the beam-steering system 400of the present invention may include a reference-beam converging lens415 which may be achromatic or monochromatic. After a reference beam 25passes through the reference-beam converging lens 415, the referencebeam 25 is reflected by a beam-steering mirror system 450 before passingthrough beam-steering lenses 410 and 405. The first and secondbeam-steering lenses 410, 405 are placed such that the reference beam 25that passes through the converging lens and the first beam-steering lens410 converges in the focal plane 425 of the second beam-steering lens405. In addition, the center point 461 shown in FIGS. 15 and 16 of adeflection mirror 460 shown in FIGS. 15 and 16 is located at a distanceof one focal length 411 of the first beam-steering lens from the firstbeam-steering lens 410. Furthermore, the elemental hologram 110 to beexposed is located at a distance of one focal length of the secondbeam-steering lens 406 away from the second beam-steering lens 305.

In another embodiment, depicted in FIG. 14, the beam steering system 400of the present invention may include a beam-steering aperture 430 whicheliminates the need to have a reference beam masking plate. In anembodiment, a reference beam 25 passes through a beam-steering aperture430 that has the aperture of the area of the elemental hologram 110 tobe exposed. If the reference beam passes through lenses that magnify orminify it, then the beam-steering aperture 430 should be sized such thatthe cross-section of the reference beam that intersects the elementalhologram to be exposed has the same size and shape of the elementalhologram. The reference beam 25 then passes through two aperture relaylenses 435, is reflected off of a deflection mirror 460 (shown in FIGS.15 and 16) of the beam-steering mirror system 450, passes through thefirst beam-steering lens 410, passes through the second beam-steeringlens 405, and then intersects the elemental hologram 110 to be exposed.The beam-steering aperture 430 is placed at a distance of one focallength 436 of the aperture relay lenses from one aperture relay lens435. The aperture relay lenses 435 are located two focal lengths 436 ofthe aperture relay lens away from each other. Then the center point 461(shown in FIGS. 15 and 16) of the deflection mirror 460 (shown in FIGS.15 and 16) is located at a distance of one focal length 436 of theaperture relay lens away from the second aperture lens 435 that thereference beam passes through.

Another embodiment of a reference beam-steering system 400 isillustrated by FIGS. 17, 18, and 21. In this embodiment, an opticalcoupler lens 670 channels a reference beam 25 that has just passedthrough a beam shutter to the fiber optic end 660 of a fiber optic cable650. The fiber optic cable 650 delivers the reference beam 25 to a fiberoptic tip 655 which is placed in the focal plane 425 of a secondbeam-steering lens 405. The reference beam 25 passes through abeam-steering lens 405 to an elemental hologram 110. The beam-steeringlens 405 is located at a distance of one focal length 406 of the secondbeam-steering lens from the elemental hologram 110 being exposed. Thefiber optic tip 655 is translated by a translation system, generally600.

FIG. 19 illustrates another embodiment of the reference beam-steeringsystem 400. In this embodiment, three reference beams 25 which may eachbe a different color are channeled by three optical coupler lenses 670toward three fiber optic ends 660 of three fiber optic cables 650. Thefiber optic cables 650 deliver the reference beams 25 to fiber optictips 655 to direct the reference beams 25 into optical combiner unit640. Optical combiner unit 640 may have two dichroic combiners 215,which may combine the three reference beams 25 into a single referencebeam 25, other suitable optical combiners. The optical combiner unit 640is placed in the focal plane 425 (shown in FIG. 17) of a beam-steeringlens 405. The single reference beam 25 from the optical combiner unit640 passes through the beam-steering lens 405 to an elemental hologram110. The beam-steering lens 405 is located at a distance of one focallength 406 of the beam-steering lens from the elemental hologram 110being exposed. The optical combiner unit 640 is fixedly mounted to aplatform 630 which is fixedly mounted to a second movable support 622.

In another embodiment, three reference beams 25 are transmitted by fiberoptic cables 650 to a optical combiner unit 640. The single referencebeam 25 that is output from the optical combiner unit 640 is channeledby an optical coupler lens 670 into a single fiber optic cable 650 whichis attached to and carried by an attaching device to a translationsystem 600. The fiber optic tip 655 of the single fiber optic cable 650is located in a focal plane 425 of a beam-steering lens 405.

In still another embodiment, the three reference beams 25 aretransmitted by fiber optic cables 650 to a optical combiner unit 640.The single reference beam 25 that is output from the optical combinerunit 640 passes through a beam shutter 225 before it is channeled by anoptical coupler lens 670 into a single fiber optic cable 650 which isfixedly attached to a translation system 600. The fiber optic tip 655 ofthe fiber optic cable 650 is located in a focal plane 425 of abeam-steering lens 405.

The translation system 600, as depicted in FIG. 18 and FIG. 19, is ableto translate in two orthogonal directions. The translation systemincludes a x-translation stage and a y-translation stage.

One illustrative embodiment of a x-translation stage 680 includes afirst lead screw 602 which is rotatably mounted by bushing, bearing, orother rotatable means to first end plates 608, and which may be rotatedabout the axis 601 of the first lead screw by a motor 604 for the firstlead screw which is fixedly mounted to one of the first end plates 608.Two first guide bars 610 are fixedly mounted to the first end plates 608such that the first guide bars 610 lie parallel to the axis of the firstlead screw 601. The two first guide bars 610 pass through two holes in afirst movable support 612. The first lead screw 602 is threaded througha hole in the first movable support 612. Thus, in this embodiment of thex-translation stage 680, when the first lead screw 602 is rotated by themotor 604 for the first lead screw, the first movable support 612 willmove along the axis 601 of the first lead screw.

One illustrative embodiment of a y-translation stage 680 includes asecond lead screw 618 which is rotatably mounted by bushing, bearing, orother rotatable means to second end plates 614, and which may be rotatedabout the axis 617 of the second lead screw 618 by a motor 620 for thesecond lead screw which is mounted to one of the second end plates 614.The other of the second end plates 614 is mounted to the first movablesupport 612 such that the axis 617 of the second lead screw isorthogonal to the axis 601 of the first lead screw. Two second guidebars 616 are fixedly mounted to the second end plates 614 such that thesecond guide bars 616 lie parallel to the axis 617 of the second leadscrew. The two second guide bars 616 pass through two holes in a secondmovable support 622. The second lead screw 618 is threaded through ahole in the second movable support 622. Thus, in this embodiment of they-translation device 690, when the second lead screw 618 is rotated bythe motor for the second lead screw 620, the second movable support 622will move along the axis 617 of the second lead screw.

The motors 604 and 620, for the first and second lead screws which maybe, but are not limited to stepper, DC servo or linear motors, may becontrolled by a motor controller 606 for the motors for the lead screwswhich may be controlled by computer 230.

Although the types, focal lengths, and number of beam-steering lensesmay be varied, for some embodiments, it may be desirable for thebeam-steering lenses to be achromatic and have f-numbers of around 3.0or less. In other embodiments, it may be desirable for the beam-steeringlenses to be achromatic, confocal, f-θ lenses, which are also known asflat-field laser-scan lenses. In some embodiments, it may also bedesirable to have lenses of lower f-number to allow for a wider range ofreference beams. In one particular embodiment, it may be desirable tohave the beam-steering lenses be achromatic and have f-numbers of around1.0. In addition, the beam-steering lenses may be monochromatic in otherembodiments.

The beam-steering system of the present invention may be utilized tocreate holographic stereograms that display a particular image whenilluminated by an illumination source from one angle, but displayanother image when illuminated by an illumination source from anotherangle. For instance, after exposing an elemental hologram with an objectbeam conditioned with a particular image on an SLM and a reference beamat a particular angle, the elemental hologram may then be exposed to anobject beam conditioned with another image on the SLM and a referencebeam at another angle. In addition, a set of elemental holograms on aholographic recording material may be exposed by a reference beam at aparticular angle, while another set of elemental holograms may beexposed by a reference beam at another angle. Thus, a printer of thisinvention can create a holographic stereogram that displays a differentimage depending on the angle of the illumination source. Furthermore,the same printer with a beam-steering system may be used to createmultiple holographic stereograms, each with a different reference angle,such that the images of each will only appear when illuminated by anillumination source at the correct angle. If such multiple holographicstereograms are mounted on top of each other, then different images maybe displayed by simply changing the angle at which the illuminationsource intersects the holographic recording materials.

Another embodiment of the present invention, illustrated by FIG. 20,utilizes multiple SLMs 90 to produce full-color holographic stereograms.In FIG. 20, two dichroic combiners 215 in an “x” configuration, or othersuitable optical combiners, may be used in combination with three objectbeams 20, one object beam being red light, the other green light, andthe other blue light. The three object beams 20 may be directed throughthree separate gray-scale SLMs 90. In one embodiment of the presentinvention the SLMs are LCD panels of high resolution such as 1,280×1,024pixels where the total size of the LCD panel is approximately 10 cm×10cm. However, smaller LCD panels may be used. For instance, LCD panelswith the same or fewer number of pixels but that are around 2 cm×2 cm insize or smaller may be used.

In an embodiment shown in FIG. 20 and FIG. 21, after passing throughbeam shutters 225, object beams 20 are directed through optical couplerlenses 670 to converge at fiber optic ends 660. The object beams 20 arethen transmitted by fiber optic cables 650 to the fiber optic tips 655which are placed in the focal planes of singlet lenses 705. The objectbeams 20 may pass through the singlet lenses 705, if necessary, reflectoff mirrors 40, and pass through SLMs 90 and band-limited diffusers 45,which may be color specific. The singlet lenses 705 expand and collimatethe object beams 20 such that the object beams 20 may more evenlyilluminate the SLMs 90. The object beams 20 are then directed through aoptical combiner unit 640 that may use two dichroic combiners 215 in an“x” configuration, or other suitable optical combiners, to combine thethree object beams 20 into a single beam. The single object beam 20 maythen pass through a first projection lens 715 and a Fourier transformfilter 710 that may remove undesired effects such as, but not limitedto, high frequency image components such as pixel or grid artifacts thatresulted from an SLM display with pixels. The object beam 20 may thenpass through a second projection lens 720 and then a converging lens 55.The first projection lens 715 is located such that images of the SLMsall lie in the focal plane of the first projection lens. The Fouriertransform filter 710 is located in the focal planes of both the firstprojection lens and the second projection lens. The converging lens 55is located such that its focal plane intersects the holographicrecording material 70 at the elemental hologram 110 to be exposed. Inother embodiments of the object beam unit 700, the first and secondprojection lenses 715 and 720 and the Fourier transform filter 710 arenot used. In still other embodiments of the object beam unit 700, avoxel control lens 500 may be included in the object beam unit 700 andlie in close proximity to the holographic recording material 70.

In one embodiment of the present invention, a material holder, generally300, may be used to translate holographic recording material 70. Asdepicted in FIGS. 22-25, a material holder 300 may include a frame 324attached to a x-translation stage 680 that is attached to ay-translation stage 690.

An embodiment of the y-translation stage 680, as depicted in FIGS.22-25, may have first holder end plates 302 to which first holder guiderods 306 are fixedly attached. A first holder lead screw 308 and a firstholder driven lead screw 309 are rotatably attached by bushing orbearing or other suitable means to the first holder end plates 302. Thefirst holder lead screw 308 and the first holder guide rods 306 areparallel to the axis of the first holder driven lead screw 307. Thefirst holder driven lead screw 309 may be rotated by a motor 310 for thefirst holder driven lead screw, which is controlled by holder motorcontroller 305, which is controlled by computer 230. The motor 310 mayalso drive both lead screws 308 and 309 with a timing belt or otherlinkage. In addition, two motors 310, each coupled to a lead screw, maydrive the lead screws. The first holder driven lead screw 309 passesthrough a threaded hole in the a first holder movable support 312. Thetwo first holder guide rods 306 in close proximity to the first holderdriven lead screw 309 pass through holes in the same first holdermovable support 312. The first holder lead screw 308 passes through athreaded hole in another first holder movable support 312, and the twofirst holder guide rods 306 in close proximity to the first holder leadscrew 308 pass through holes in the same first holder movable support312.

An embodiment of the x-translation stage 680, as depicted in FIGS.22-26, may have a second holder lead screw 318 and a first holder drivenlead screw 319 rotatably attached by bushing or bearing or othersuitable means to second holder end plates 314. The axis of the secondholder driven lead screw 317 is orthogonal to the axis of the firstholder driven lead screw 307. The second holder lead screw 318 and thesecond holder guide rods 316 are parallel to the axis of the secondholder driven lead screw 317. The second holder driven lead screw 319may be rotated by a motor 320, for the second holder driven lead screwwhich is controlled by holder motor controller 305, which is controlledby computer 230. The second holder driven lead screw 319 passes througha threaded hole in the a second holder movable support 322. The twosecond holder guide rods 316 in close proximity to the second holderdriven lead screw 319 pass through holes in the same second holdermovable support 322. The second holder lead screw 318 passes through athreaded hole in another second holder movable support 322, and the twosecond holder guide rods 316 in close proximity to the second holderlead screw 318 pass through holes in the same second holder movablesupport 322.

As depicted in FIGS. 22 and 23, the x-translation stage 680 may bemounted to the y-translation stage 690. In one embodiment, the firstholder movable supports 312 are fixedly mounted to the second holder endplates 314. The second holder movable supports 322 are fixedly attachedto a frame 324. A second frame 324 may be clamped to a first frame 324by detachable couplings 325 which may include, but are not limited to,clamps, snaps, screws, and bolts. A holographic recording material maybe held in between two detachably coupled frames 324. In an alternativeembodiment, the natural adhesive property of a holographic recordingmaterial may hold the material on one side of a transparent plate thatis secured to frames 324. The frames 324 may be composed ofstress-relieved aluminum, titanium, composites, or other rigid, strong,and lightweight materials.

As illustrated in FIG. 23, object beam units 700 and referencebeam-steering systems 400 may be fixed to bases 326.

As illustrated in FIGS. 24 and 25, one or more object beam units 700 maybe fixedly mounted to unit mounts 328 which are fixedly mounted tosecond holder movable supports 322 of a x-translation stage 680.Similarly, one or more reference beam-steering systems 400 may befixedly mounted to other unit mounts 328 which are fixedly mounted toother second holder movable supports 322 of another x-translation stage680. In addition, in some embodiments, a frame 324 may be fixed to thefirst movable supports 312 of a y-translation stage 690. Thus, in someembodiments, the holographic recording material 70 clamped between twoframes 324 may translate vertically, while the object beam units 700 andreference beam-steering systems 400 translate horizontally.

In the embodiment depicted in FIG. 24, two motors 320, which arecontrolled by holder motor controller 305, drive the second holderdriven lead screws 319 of the x-translation stages 680. In analternative embodiment depicted in FIG. 25, one motor 320, incombination with a timing belt 330 that is linked to a belt mount 332that is fixedly attached to one of the second holder driven lead screws319, drives both second holder driven lead screws 319 of thex-translation stages 680.

In another embodiment depicted in FIG. 26, the object beam units 700 andreference beam-steering systems 400 are attached to unit mounts 328which are attached to the second holder movable supports 322 ofx-translation stages 680. A holographic recording material 70 translatesvertically by a y-axis roller system 350 with rollers 342 and 344. Theholographic recording material 70 may be wrapped around a top roller 342and a bottom roller 344. The top and bottom rollers 342 and 344 arerotatably mounted by bushing, bearing, or other suitable means betweenroller end plates 340. The top roller 342 may be rotated by a motor forthe rollers 346, which is controlled by a motor controller 305 which iscontrolled by a computer 230.

The motors used in the various embodiments of the translation systemsmay be, but are not limited to stepper motors.

As depicted in FIGS. 23-26, there may be simultaneous or parallelprinting of elemental holograms. In some embodiments, the printer mayinclude object beam units and reference beam-steering systems attachedto translation systems with x-translation stages that are attached toy-translation stages. In such systems, the holographic recordingmaterial may be fixed, while the object beam units and referencebeam-steering systems are moved by the translation system to record anarray of elemental holograms.

In an alternative embodiment, multiple layers of holographic recordingmaterial 70 may be held in a material holder 300. In addition, eachlayer may be sensitive to a particular wavelength of light.

In another embodiment of the present invention, for a given object beam,a matched set of a band-limited diffusers 45 and a reference beammasking plate 65 may be configured to allow for even exposure of anelemental hologram 110 of a particular size or shape and to preventexposing portions of the holographic recording material 70 that are notpart of the elemental hologram 110 intended to be exposed. Asillustrated by FIGS. 27( a), (b), and (c), matched sets of band-limiteddiffusers 45 and reference beam masking plates 65 can be constructed toallow the exposure of elemental holograms 110 of different sizes orshapes. If the sets of band-limited diffusers 45 and reference beammasking plates 65 are constructed such that the band-limited diffusers45 of all the sets have the same outer dimensions and can be placed inthe same position in a hologram printer, and such that the referencebeam masking plates 65 of all the sets have the same outer dimensionsand can be placed in the same position in a hologram printer, then setscan be conveniently switched to easily change the size of the elementalhologram printed. Thus, a matched set of a band-limited diffuser 45 anda reference beam masking plate 65 can be replaced with another set of aband-limited diffuser 45 and a reference beam masking plate 65 so as toallow printing of a larger, smaller, or differently shaped elementalhologram. As depicted in FIG. 27( b), a band-limited diffuser 45 may bemounted onto a plate 510 housed in a threaded frame 515. The plate 510may be a sheet transparent sheet of glass with an anti-reflectivecoating. The threaded frame 515 may be threaded into positioning device525 which has a base 526 and a threaded ring 520. The positioning device520 may allow translational adjustment in three orthogonal directions bythree adjustable screws 530. As depicted in FIG. 27( c), a referencebeam masking plate 65 may be housed in a threaded plate frame 560. Athreaded plate frame 560 may be threaded into a threaded positioningdevice 565.

Some examples of full-color embodiments of the present invention aredepicted in FIGS. 7, 8, 19, and 21. Another embodiment of the presentinvention includes a full-color printer with three different coloredlasers, optical combiners, such as but not limited to dichroiccombiners, to combine the three beams from the lasers, a full-color SLM,and achromatic optics to print full-color holographic sterograms. Stillanother embodiment of the present invention includes a full-colorprinter with three different colored lasers, an object beam unit thatcombines three object beams using three band-limited diffusers, threegray-scale SLMs, and an optical combiner, achromatic optics, such asachromatic lenses, to manipulate or condition the full-color beamsproduced by the printer, and an optical combiner to combine threereference beams into a combined, full-color, reference beam. Yet anotherembodiment of the present invention includes a full-color printer withthree different colored lasers, an object beam unit with an HOE thatcombines three different colored object beams into one combined,full-color, object beam and that also evenly distributes the combinedobject beam over an elemental hologram, an optical combiner to combinethree reference beams into a combined, full-color, reference beam, andachromatic optics to manipulate or condition the full-colored beams.

Another aspect of the present invention involves a method of creatinganimated, one-step, full-parallax, holographic stereograms. Oneembodiment involves using multiple or sub-divided viewing zones, whichtypically are not needed to produce static image, full-parallaxholographic stereograms, to produce one-step, full-parallax, holographicstereograms that can display animated subjects or different imagesthrough different viewing zones. Viewing zones are typically planarareas located at a distance from the holographic recording material inwhich a viewer's eye looking through that plane could see theholographic image produced by an array of elemental holograms. Thus, aviewing zone may be analogous to a window in front of a hologram.However, rather than being planar, viewing zones may also be constructedfrom a series of points. Unlike traditional techniques for producingone-step, full-parallax holographic stereograms in which the view of athree-dimensional object or a scene is determined for each elementalhologram, the present invention produces animated, one-stop,full-parallax holographic stereograms by determining the view of anobject or scene that an observer would see in each viewing zone.

Referring to FIGS. 28-31, and assuming that a voxel-control lens 500 isused such that the image 505 (shown in FIG. 10( b)) of an SLM wouldappear at an infinite distance from the surface of the holographicrecording material, the steps for producing a holographic element of ananimated holographic stereogram or a holographic stereogram thatdisplays different images in different viewing zones are as follows.

-   -   1) Select the size and shape of a holographic stereogram, and        the size and shape of its elemental holograms.    -   2) Select the desired effect. One example of an effect is        changing the orientation of an object or a scene (e.g., its        position or rotation) when a viewer moves. Another example of an        effect is changing the shape or color of an object or a scene        when a viewer moves.    -   3) Select the reference illumination geometry for the final        holographic stereogram.    -   4) Select the shape(s), size(s), and location(s) of the viewing        zone or zones with respect to the holographic recording        material. In the plane of the viewing zone, a viewer would see a        sharper transition between the different objects or scenes        depicted by the holographic stereogram than a viewer not in the        plane of the viewing zones. Thus, it may be desirable to select        the location of the viewing zones to be at a distance from the        holographic recording material where most viewers would be        located.    -   5) Select the objects or scenes or the attributes of the objects        or scenes to be displayed by the holographic stereogram.    -   6) Select the location and placement with respect to the        holographic recording material of the holographic images of the        objects that will be displayed by the holographic stereogram to        be created (i.e. whether the image will be located in front of,        in back of, or straddle the holographic recording material).    -   7) Using a computer 230, generate computer models and model        attributes for each viewing zone using traditional computer        graphic techniques and programs of the objects or scenes. For        instance, generate a computer model of an object ‘A’ 835 which        can only be seen from one viewing zone 805, and generate a        computer model of an object ‘B’ 840 which can only be seen from        another viewing zone 810.    -   8) Set up the hologram printer. For instance, put holographic        recording material 70 (shown in FIG. 7) into a material holder        300 (shown in FIG. 7), calibrate and initialize beam shutters        225 (shown in FIG. 7), motor controllers 305, 455 the SLM 90        (shown in FIG. 7), the beam-steering system 400 (shown in FIG.        7), and initialize the computer graphics program, and the        computer 230 (shown in FIG. 7).    -   9) Using a computer 230, for each elemental hologram 110 in a        holographic stereogram that may be a one-step, full-parallax,        holographic stereogram:        -   A) Project lines from the perimeter of the elemental            hologram 110 through the perimeter of each of the view zones            805 and 810. Since in a typical printer, a SLM is usually            centered in front of an elemental hologram when the            elemental hologram is exposed, the virtual image of the SLM            that an elemental hologram would see through a voxel-control            lens is also usually centered in front of the elemental            hologram, as shown in FIG. 29. As depicted in FIG. 30, the            projected lines intersect a virtual two-dimensional image            505 (shown in FIG. 10( b)) of a SLM image. The elemental            hologram will only see the portion of the virtual image 505            of the SLM, such as 815 or 820, bounded by the projecting            lines. As shown in FIG. 30, the projected lines define mask            volumes 825, 830, which may differ from one elemental            hologram to another for a given viewing zone.        -   B) For a desired viewing zone mask volume, such as 825, for            an elemental hologram 110, using traditional rendering            techniques, such as but not limited to, ray-tracing or            scan-line conversion, render the portion of the appropriate            computer model of an object or scene 835 (shown in FIG. 30)            enclosed by the projected mask volume 825 to create a            complete two-dimensional image of a projection on the            portion of the virtual image 505 of the SLM of the computer            graphic models of the objects or scenes 835 or 840 from the            perspective of an elemental hologram. For instance, if a            person were to look at a particular elemental hologram from            within a mask volume 825, only the ‘A’ object 835 is seen.            From mask volume 825, the ‘B’ object 840 is not viewable.            Thus, to a viewer in mask volume 825, the bottom of the            virtual image of the SLM is not visible. Similarly, if a            person were to look at the particular elemental hologram            from within a mask volume 830, only the ‘B’ object 840 is            seen. From mask volume 830, the ‘A’ object 835 is not            viewable. Thus, to a viewer in mask volume 830, the top of            the virtual image of the SLM is not visible.        -   C) When rendering is complete for all the viewing zones 805            and 810 for an elemental hologram, composite the rendered            images for the viewing zones.        -   D) Display the composite rendered image for the viewing            zones 805 and 810 on the SLM 70 and allow light to pass            through the beam shutters 225 for the proper time period to            expose the elemental hologram.        -   E) Translate the material holder such that another elemental            hologram can be exposed.        -   F) Repeat steps A through E until all the elemental            holograms have been exposed.

In an alternative embodiment, rendering for multiple elemental hologramsmay be completed before exposing any of the elemental holograms on aholographic recording material.

In an alternative embodiment, the same method applied for creatingholographic stereograms with changing views may be used to create aholographic optical element (HOE). For instance, if it is desirable tocreate a HOE that acts like a lens to a converge diverging white lightto a point, then by using the same viewing zone method as described, butdetermining a view point located at where the light should be focused,rather than a view zone, a HOE may be created. Alternatively, such a HOEcan be created by determining a white computer-graphic object with theexact size, shape, and position of a given voxel, and printing aholographic stereogram of such an object.

In one embodiment of the present invention, the same computer 230 may beprogrammed to control the motors controlling the beam shutters, themotor controllers for the beam-steering mirror system, the motorcontrollers for the translation systems, conducts the computer graphicscreation and rendering, and controls the display of the SLM. In analternative embodiment, the same computer may also conduct thecomputations necessary for animation. The computer 230 may be connectedto the beam shutters, the motor controllers for the beam-steering mirrorsystem, and the SLM, through cables connected at both ends to serial orparallel communication ports. One end of the cables may be connected tothe communication ports of the computer and the other ends of the cablesmay be connected to the devices controlled by the computer. In otherembodiments, multiple computers 230 may be used.

While the methods and apparatus of this invention have been described interms of illustrated embodiments, it will be apparent to those of skillin the art that variations, such as but not limited to differentcombination of lens set-ups to create the same effect as thevoxel-control lens or the beam-steering lenses described herein, may beapplied to the methods and apparatus and in the step or in the sequenceof steps of the methods described herein without departing from theconcept, spirit and scope of the invention. All substitutes andmodifications apparent to those skilled in the art are deemed to bewithin the spirit, scope and concept of the invention as defined by theappended claims.

1. An apparatus for printing holographic stereograms comprising: a lightsource that produces a coherent beam: a beam splitter that splits thecoherent beam into an object beam and a reference beam; a materialholder holding a holographic recording material having elementalholograms; an object beam unit for displaying a rendered image and forconditioning the object beam with the rendered image to interfere withthe reference beam at a chosen elemental hologram; a referencebeam-steering system for directing the reference beam to interfere withthe object beam at the chosen elemental hologram; and a computerprogrammed to control the interference of the object beam and thereference beam and the delivery of the rendered image to the object beamunit. 2.-62. (canceled)